The whole idea of these unlicensed bands is that there are limits on power and such, and otherwise you can more or less do what you want as long as you're not deliberately interfering with other people. If your legitimate use happens to step on other people's legitimate use, well, so it goes. If you want to make sure nobody else can interfere with you, use a licensed frequency and obtain a license for your use.

I think this raises an interesting point. There ought to be some frequency bands accessible by common WiFi hardware which require a license to use. Then big venues like this could set up their networks on licensed bands, after obtaining a license, and be free from interference by people's mobile hotspots and such.

Although I have a feeling that approximately nobody would actually go through the process of getting a license, because the whole "interference" thing is just a cover, and their actual motivation is a cash grab by attempting to force people to use their spectacularly overpriced service.